Resonators in the form of a passive component can be used as a channel filter in radio transmission links. Channel filters used in practice usually consist of a plurality of coupled resonators. With increasing frequency of the signal transmission on a radio link, the requirements on the filter change, in particular the structural and spatial requirements on the one hand as well as the demands on the usable bandwidth of a filter. The usable bandwidth here is that frequency bandwidth at which a filter response around a central frequency is constant or nearly constant.
Depending on the resonant frequency of a filter, it is usually necessary to adjust, for example, the geometrical dimensions of a filter.
Channel filters may be used, for example, in so-called output multiplexers. A typical output multiplexer comprises channel filters, which are connected to a waveguide busbar. One object of the output multiplexer is to combine narrowband high power communication signals on a common waveguide (the so-called busbar). The channel filters and busbar are coordinated in a complex development process. The individual parts for the channel filters as well as the busbar and any necessary additional parts can usually only be ordered and manufactured after the end of this development process.
In the currently commonly used Invar circular waveguide technology, as well as all other available technologies, various complex construction and development processes are to be observed, as these devices may comprise many customized individual parts. The individual parts must usually be individually manufactured and procured for each channel filter. By means of the adjusting screws which are provided in this technology, a fine adjustment of the resonant frequency in the range of a few parts per thousand of the resonant frequency can occur. However, a free setting of the filter frequency (resonant frequency) is not possible.
With the TE01n mode, which is frequently used for the temperature compensation of aluminum filters, it is possible in contrast to displace a complete end wall of the resonator, as these modes do not require wall currents from side walls to the end wall. This structure is usually used for the compensation of temperature influences.